The invention relates to a marine drive having dual counter-rotating coaxial propellers.
Dual propeller marine drives with concentric counter-rotating propeller shafts are known in the prior art. The present invention provides improvements thereover, particularly in performance and durability.
In one aspect of the invention, cavitation of the propellers is provided by through-propeller-hub exhaust structure which is simple and rugged. An exhaust passage in the drive housing communicates with the lower horizontal bore in the torpedo of the housing. The exhaust passage communicates with the bore at the bearing carrier spool which supports the dual propeller shaft assembly. A passage through the spool passing exhaust rearwardly therethrough. The spool is provided by a cylindrical member having a first outer diameter portion engaging the housing within the horizontal bore, a second reduced outer diameter portion within the horizontal bore and aft of the first outer diameter portion and defining an annular recess receiving exhaust from the first exhaust passage in the drive housing, a third outer diameter portion aft of the second outer diameter portion and engaging the housing and having a plurality of slots extending rearwardly therethrough, and a fourth reduced outer diameter portion aft of the third outer diameter portion and external of the horizonal bore, such that exhaust from the annular recess flows rearwardly through the slots through the third outer diameter portion then rearwardly through the propeller hubs.
In another aspect, oil passage structure is provided for lubricating the dual propeller shaft assembly. An oil passage is provided by another passage in the drive housing, which passage communicates with the lower horizontal bore forwardly of the exhaust passage. The passages are sealed from each other by the spool which has an annular seal engaging the housing within the horizontal bore at a location axially between the passages. The spool is thread mounted within the horizontal bore. A locking ring is thread mounted in the horizontal bore and is tightened against a tapered roller thrust bearing supporting the driven gear on the outer propeller shaft engaged by the pinion gear of the vertical drive shaft. The threaded locking ring is spaced forwardly of the forward end of the carrier spool by an axial gap. The oil passage in the housing communicates with the horizontal bore at the axial gap and lubricates the dual propeller shaft assembly, including a bearing between the outer propeller shaft and the spool, and a bearing between the inner and outer propeller shafts.
The invention further relates to commonly owned copending allowed application Ser. No. 07/889,530, filed May 27, 1992, U.S. Pat. No. 5,249,995, allow application Ser. No. 07/889,495, filed May 27, 1992, U.S. Pat. No. 5,230,644, and allowed application Ser. No. 07/892,399, filed May 28, 1992, U.S. Pat. No. 5,236,380, incorporated herein by reference, and to application Ser. No. 08/069,163, filed on even date herewith and which is a continuation-in-part of the present application.